Open Window, Dialog or Message Box from a ViewModel – part 1

Saying that a view-model belongs to the Application layer, and the Application layer doesn't references upper layers, and must not create or use visual objects, how can I open a Window, Dialog or any kind of Message Box on-the-fly, based on some logic triggered by the view or view-model? Well, there are several options doing that, one is using kind of service which encapsulates that, providing an